The invention relates to use of selective oxidation of silicon in memory cells and arrays. Selectively oxidizing silicon while avoiding oxidation of exposed tungsten and tungsten nitride has been used in CMOS devices formed in monocrystalline silicon, as described by Liu et al., “Selective Oxidation of Silicon (100) vs. Tungsten Surfaces by Steam in Hydrogen,” Journal of the Electrochemical Society, 150 (10) G597-G601, 2003, hereby incorporated by reference. This technique can be extended to address challenges that arise in diode memory arrays, thin film transistor (TFT) memory arrays, and monolithic three dimensional memory arrays.